This invention relates to writable electronic tablets that allow users to take notes, draw figures, and edit documents electronically. In some embodiments, the writable electronic tablets record the writings/drawings and convert them into a digital format that is easily saved, recalled, and shared. In some embodiments, the writeable electronic tablets merely provide an alternative format to take notes, draw designs, and leave messages.
A number of LCD-based tablets are commercially-available that have the ability to record a user's writing, drawing, or mark-up of documents. For example, the Microsoft SURFACE® Pro 4 (Microsoft Corporation, Redmond, Wash.) comes with a stylus (SURFACE PEN®) that allows a user to take notes, draw, and mark-up documents that are viewed on the LCD touch screen. The position of the stylus is tracked by broadcasting a signal from the stylus tip to the capacitive touch screen of the tablet, whereby a proximity-sensing algorithm is used to determine the location of the stylus. Other LCD-based tablets, such as the Sony VAIO LX900 (Sony Corporation, Tokyo, Japan) use the digitizing technology of Wacom (Wacom Co. Ltd., Kazo, Japan) whereby the stylus tip (including an inductive loop) is located by an energized digitizing layer located behind the LCD display. The digitizing layer typically comprises a grid of overlapping electrodes adjacent a magnetic film. The stylus head in the Wacom system includes an inductive coil, and the motion of the coil during writing can be translated into a position with respect to the grid defined by the electrodes in the digitizing layer.
A common complaint from users is that these LCD-based tablets do not provide a “paper-like” experience. First, because the LCD is power-hungry, the screen will often go dark when the tablet is not in active use. This means that a user has to “wake up” the device to start writing, and sometimes has to reawaken the device during a writing session because the device went “to sleep” while the user was listening to a speaker, or otherwise engaged in a different task. Secondly, the pen strokes do not feel or look like writing on paper because the texture, depth, and latency of the writing device is perceptibly different that using a pen on real paper. Often when writing on an LCD display with a stylus, a user has the sense that he/she is dragging a plastic stick across a plate of glass. Furthermore, when using these types of electronic tablets, the writing has a “depth” into the viewing surface that is disorienting. The written words are not at the top surface interacting with the stylus, but rather disconnected from the stylus tip.
Alternate electronic writing devices have been constructed using light-reflective media, such as electrophoretic ink (E Ink Corporation, Billerica, Mass.). See, for example, the DPTS1™ from Sony (Sony Corporation, Tokyo, Japan). Electrophoretic ink solves many of the “sleeping” problem of LCD-based writing systems because the devices are always “on”. They consume far less power during the writing process so they don't need to go to sleep except when prompted by the user, and even after they are asleep they continue to display the writing. Additionally, because the electrophoretic ink is very close to the surface of the device, the pen response looks more like writing. The devices are also sunlight-readable, which makes it possible to use the device outdoors or in other bright-light environments. Some commercially-available electrophoretic ink devices, such as the ReMARKABLE™ tablet (REMARKABLE A.S., Oslo, Norway), also include high-friction surface materials that create a “feel” that is far more paper-like. While such friction materials can be included on LCD displays, the materials can interfere with the image quality of the LCD because the friction materials scatter the light emitted from the display.
Regardless of the format (LCD or electrophoretic ink), users of electronic (tablet) display writing systems typically experience distracting latency between stylus movement and image updates when writing. This latency is caused by the time that is required to sense the position of the stylus and update the image driver so that the movement of the stylus is accurately portrayed as writing/drawing on the screen. The latency is the additive delay of a series of steps such as sensing the position of the stylus, sending the position information to the display driver, processing the display change, and refreshing the display. In many cases, the position information is additionally saved to memory to allow the user to later recall the notes, and this saving step may add an additional small delay. In LCD-based systems, the latency is typically on the order of 60 ms. Many users find the latency to be distracting, and in some cases, the latency limits the speed that a user can take notes, draw, etc.
In addition to the sensing and saving the position information, there may be additional lag time associated with refreshing the image to show the writing. For example, electrophoretic ink systems often have latencies of at least 100 ms because of the additional time (20-40 ms) that it takes to drive the electrophoretic particles between image states after the update is sent to the pixels. In addition, the latency may vary depending upon what portion of the display is being updated. That is, the latency is different across the display surface because the display driver updates the scan lines in an orderly fashion. For example, the latency may be more noticeable when writing in the lower right-hand corner of a tablet versus the upper left-hand corner.
To counter the latency, some manufacturers use predictive algorithms to reduce the number of updates needed to capture the writing. These predictive algorithms may, for example, process the previous letters that were written and predict the next letters. The algorithms may also employ a rolling average to anticipate straight lines or use smoothing to account for fluctuations in stylus sensing. Nonetheless, such algorithms can result in unintended strokes being generated which can be just as distracting to a user as waiting for updates.